Fiber in the Diet?

Fibre in the Diet for Cats and Dogs

A necessity or fad?

Fiber is the part of plants that cannot be digested. As a result, it provides zero calories and passes through the digestive system virtually unchanged, but along the way it serves some crucial roles.

Fiber absorbs water like a sponge. This means that if there is excess water in the colon, for example during diarrhea, any dietary fiber will soak it up and help to produce a firm stool. If, on the other hand, there is too little water in the colon, which often leads to constipation, the fiber will draw water in from surrounding tissues and help to resolve the problem. As you can see, fiber is important in maintaining intestinal health and can effectively treat both constipation and diarrhea.

Another important function of fiber is as a prebiotic. This means that is provides a medium and a food source for “friendly” intestinal bacteria. These bacteria aid in the digestion of food and help to prevent harmful bugs from getting established.

Dietary fiber also slows down the digestion of the other foods it is consumed with. This can be particularly useful in diabetic dogs because the fiber helps to provide a slow, steady release of dietary sugar into the bloodstream. It can also help with weight loss programs as foods that are high in fiber are digested more slowly, allowing the dog to feel fuller for longer while providing less calories.

Although dietary fiber is not classed as a nutrient ​1​, and not considered an essential component of a diet, it is important and does affect the health and efficient functioning of the gut in several ways:

  • It delays gastric emptying;
  • It alters nutrient absorption and metabolism;
  • It normalizes transit time through the gut;
  • It maintains the structural integrity of the gut mucosa;
  • It increases the water-holding capacity of the feces;
  • It adds bulk to the feces.

Dietary fiber does have disadvantages:

  • Flatulence and stomach rumble – particularly when large quantities are introduced suddenly into the diet;
  • Increased fecal output.

In addition, decreased digestibility of protein, fat and carbohydrates, together with decreased uptake of some minerals, could lead to inadequate intake of these minerals under some circumstances.

In the wild, carnivores tend to eat all parts of their prey, both digestible and indigestible, so fiber can be regarded as a natural part of the diet. Fiber is only found in plants, so virtually all vegetables contain some, while meats contain none at all.

Dietary Fiber Requirements

Dietary fiber affects carbohydrate digestion and absorption. Typical commercial grain-based pet food dietary fiber consists of plant materials such as cellulose, hemicellulose, lignin, and pectins. Non-plant-cell-wall sources of fiber such as gums, mucilages, algal polysaccharides, and modified cellulose are also added to McKibble and McCan ​2​. Dietary fibers are insoluble or soluble. Insoluble fibers consist primarily of cellulose and some hemicelluloses. They also include lignin which represents a small part of dietary total fiber. Insoluble fibers are the structural building material of cell walls. This fiber’s major source is the bran part of cereal grains. Colonic bacteria do not ferment most insoluble fibers.

Classification of Dietary Fiber

InsolubleSoluble
Cellulose: whole-wheat flour, bran, vegetablesHemicellulose: psyllium seed
Hemicellulose: bran, grainsPectin: fruits
Lignin: wheat, vegetablesGums: oats, legumes, guar, barley

Ferment-ability of Dietary Fiber

HighLowModerate
cellulosebeet pulppectin
methylcellulosegum arabicguar gum
wheat branrice brancabbage fiber
locust bean gumxanthum gum

Water soluble fibers are all other non-structural and indigestible plant carbohydrates. Soluble fibers such as pectin, guar gum, and carboxymethylcellulose absorb water and form gels; they slow gastric emptying, reduce nutrient absorption, and increase intestinal transit rate. Increased dietary fiber reduces digestibility for carbohydrates, proteins and fats and affects absorption for some vitamins and minerals. Water insoluble fibers such as wheat cereal bran and cellulose reduce digestion and absorption the least. Fiber increases fecal volume and promotes more frequent defecation. Fiber from cereal grains also increases fecal volume by absorbing water.

Fiber Fermentation

Colonic bacteria vary in their ability to ferment fiber. Wheat bran and cellulose fiber are poorly fermented. Beet pulp, rice bran, and some gums are moderately fermented. Pectin, guar gum, oat bran, and some vegetable fibers are readily fermented. As mentioned, fermentation maintains greater numbers of colonic bacteria and produces short-chain fatty acids, some of which are important for colonic nutrition. Fatty acids also promote colonic salt and water absorption. Excess fermentable fiber causes diarrhea due to the presence of large amounts of short-chain fatty acids. Fibre added to commercial grain-based diets can be completely unfermented such as cellulose flour and poorly fermented such as wheat bran. They do little more than increase fecal volume. Some added fibers are jelling agents such as guar gum, alginates, etc. which are typically added to canned commercial dog foods that contain gravy and real or simulated meat chunks. Colonic bacteria readily ferment jelling agents, but excessive amounts can cause diarrhea.

The Fiber Debate …

Fiber has been a component of McKibble and McCan during the last 50 years as the trend developed to no longer feed owner-prepared or raw food diets. In the past, pet parents rarely add fiber to foods they prepare. The “old way of doing things” seemed to have provided adequate fiber in the diet to supply colonic nutritional needs. However, based on today’s research available, as a result of the commercial pet food industry, feeding a mostly meat diet would seem to supply inadequate fiber, if we are to believe them. Most pets receive adequate fiber because they have few gastrointestinal problems. Interestingly though, dogs and cats in the wild select diets containing negligible fiber. Thus, we have to surmise that dogs and cats have low requirements for fiber. Commercial grain-based pet food manufacturers claim that optimal dietary crude fiber levels should range from 1.4% to 5%. In contrast, there is little scientific basis for any recommendation of this nature. Canine and feline nutrition books devote entire chapters to fiber but they give no recommendation on dietary fiber levels for normal dogs or cats. An owner-prepared or biologically species appropriate diet contains less than 1.4 percent fiber, unless it contains large amounts of vegetables, beans, peas or bran-rich cereals.

Fiber is not a dietary requirement for our fur kids, but may be needed because we don’t feed our fur kids animal fur (prey model) and other non-digestible sources of fiber, so they may become constipated due to their sedentary lives.

Fiber Content of Commercial Pet Foods?

The type of fiber in commercial grain-based diets has been unimportant, other than, whether it causes diarrhea. High fiber content causing large-volume bulky bowel movements has not concerned most manufacturers. But, the pet nutrition community are in agreement that the 20 percent fiber level of some pet foods are excessive. Some manufacturers now add less fiber and use a poorly soluble (so that it does not affect digestive function) and moderately fermentable (so that it provides nutrients for the colonic mucosa but not enough fermentation of fiber to cause diarrhea) fiber. Beet pulp and rice bran are examples of such fibers. If the need for fiber is small why give an excess that can cause impaired digestive tract function, bulky bowel movements, and diarrhea?

Fiber is the source of energy for colonic mucosal cells ​3​Bacteria accomplish that by producing short chain fatty acids (acetate, proprionate and butyrate). More than 70 percent of colonic cells’ energy is dependent on these fatty acids. Fiber levels needed to meet these requirements is probably low, but the lack of unbiased research make this assumption a generalisation. Many animals live on low fiber diets for years without developing colonic disease.

Fiber for Management of Disease?

Fiber is added to McKibble or McCan designed for weight reduction. Commercial pet food companies claim this to be effective, because fibre reduces digestibility of other nutrients and supposedly reduces appetite or hunger by filling the stomach (the McKibble or McCan effect). Sometimes veterinarians vary the dietary content of fiber for other reasons, more than often feed low fiber diets to dogs with chronic diarrhea. Some vets recommend feeding high fiber diets to dogs with colitis. High fiber diets can help manage some animals with diabetes mellitus. Although veterinarians promote additional fiber in pet foods to treat these medical problems, there is little scientific evidence that additional fiber is of any value to the animal.

When to add fiber to the diet?

If you fur kids has dry, crumbly stools or difficulty pooping, then you would need to add a small amount of fiber to the diet. If not needed, don’t add it.

Ground psyllium or coconut fiber (chips or flower) are both easy ways to add insoluble fiber if needed, but often more pumpkin, butternut or veggies will take care of the problem.

Did You Know? Tripe (and tripe-based meals) are excellent sources of natural dietary fiber for your fur kids. A well formulated biologically species appropriate raw food formula for dogs should also contain a small amount of vegetable fiber in the diet, typically no more than 2% as wet / 7% as dry (DM), or raw, unwashed tripe.

What have we learned to date?

Dietary fiber (or “roughage”) applies to complex carbohydrates and the edible parts of plants that cannot be digested or absorbed in the small intestine and passes into the large intestine intact. The term “dietary fiber” also includes a type of starch known as resistant starch (found in pulses, partly-milled seeds and grains, some breakfast cereals) because it resists digestion in the small intestine and reaches unchanged the large intestine. Fiber is only found in plants – hair, hooves, bones, fish scales, and feathers do not contain any fiber. Fiber is composed of polysaccharides (complex sugars), and is found in plant cell walls, where it provides structural strength and rigidity. While fiber itself is indigestible and generally considered non-nutritive, some fibers do contain nutrients, such as vitamins and minerals, that can be extracted during digestion, either by the mechanical grinding action of the stomach and intestines, or through bacterial fermentation in the colon. However, the nutrients present in fiber are not the reason it is often included in McKibble and McCan.

Additional Articles and Resources

Additional resources and research for you.

  • Dr. Connor Bradey on Fibre and Anal Glands (DogFirst);
  • Dr. Karen Becker on the role of fibre in the diet (Mercola);
  • Fermentation of animal components in strict carnivores: a comparative study with cheetah fecal inoculum. (PubMed).

Dr. Karen Becker Discusses Dietary Fiber

References and Research

  1. 1.
    Butterwick R, Markwell P. Effect of amount and type of dietary fiber on food intake in energy-restricted dogs. Am J Vet Res. 1997;58(3):272-276. https://www.ncbi.nlm.nih.gov/pubmed/9055973.
  2. 2.
    de G, Kerr K, Fahey G. Alternative dietary fiber sources in companion animal nutrition. Nutrients. 2013;5(8):3099-3117. https://www.ncbi.nlm.nih.gov/pubmed/23925042.
  3. 3.
    Sandri M, Dal Monego S, Conte G, Sgorlon S, Stefanon B. Raw meat based diet influences faecal microbiome and end products of fermentation in healthy dogs. BMC Vet Res. December 2016. doi:10.1186/s12917-017-0981-z

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